Hybrid ring



May 19, 1953 w. D.- LEWIS 2,639,325

' HYBRID RING Filed March 24, 1950 2 Sheets-Sheet 1' IN 15 N TOR w 0. LEW/S AT ORNEY y 9, 1953 w. D. LEWIS 2,639,325

HYBRID RING Filed March 24, 1950 2 Sheets-Sheet 2 v I INVENTOR' n: p. LEW/S ATTO NEY Patented May 19, 1953 HYBRID KING 7 v Willard D. Lewis, Little Silver, N. 'J., assignor to Bell Telephone Laboratories, Incorporated, New York, N; Y a corporation of New York Application March 24, 1950, Serial N 0. 151,620

This invention relates to hybrid rings. i More particularly it relates to hybrid rings proportioned to provide favorable impedance characteristics and simplicity in construction. y

Hybrid rings constructed of portions of transmission line of the coaxial, Wave-guide or paired conductor types, are well known to those skilled in the art as illustrated, for example, by the numerous and varied species disclosed in United States patent 2,445,895, granted July 2'7, 1948, to W. A. "I'yrrell, assignor to applicants assignee. While Tyrrell employs the term duplex-balancer in describing his ring structures, those skilled in the art more frequently refer tosuch devices as hybrid rings or ring type hybrid junctions. A general description of the objective properties of a hybrid junction is given, for example, in my copending application, Serial No. 789,985, filed December 5, 1947, which matured into United States Patent 2,531,447 granted November 28, 1950. While that application is concerned primarily with the wave-guide double T type of hybrid junction, the objective properties are, for many purposes, substantially, identical with those of the ring type hybrid junction.

Referring particularly to Figs. 12 and 37 of Tyrrells Patent 2,445,895, an inconvenient, feature of'prior arthybridrings is the factthat the :im,-

pedances required for the four circuits tobe con-'1 An additional. obJect is to provide: a-hybrid-ring type junction oftransmissio'nline havinga char: acteristic impedance orzr'afidrour unction" or terminal points at each of which an impedance of Z will be found when the other three points are connected to circuits each of which-has an;

impedance of Z0.

Another object of the ,invention is to provide hybrid rings in which the above-mentioned uni formity of terminal impedances can berealized by structures consisting throughout of a single uniform size of transmission line for both the ring portion of the structure and for the terminal stubs of the structure.

A further object ofthe invention is to provide a methodjof proportionin'g a hybrid ring structure so that it can'be constructed of a single uniform type of transmission line for both the ring and the terminal stubs, and four circuits having identical impedances", differing from that of the characteristic impedance of the transmission line of which the ring structureis constructed, can be, connected to the four terminals, 'respectivelyl 'of s e ti el nof. the" Claims (01. 178-44) Other and further objects will become apparent du'ring'the course of the following description and from the appended claims.

The principles of the invention will become apparent in connection with the detailed description, given below, of the diagrams of Figs. 1 to 4, inclusive, of the accompanying drawings, and of the specific illustrative embodiments of the invention shown in the other figures of the accompanying drawings in which:

Figs. 1 to 4, inclusive, are schematic diagrams employed in the following description to facilitate explanation of the principles underlying the operation of devices of the invention;

Fig. 5 illustrates one specific embodiment of the invention, in which the hybrid ring and connecting stubs are constructed of coaxial transmission line;

I Fig. 6 illustrates a second specific embodiment of the invention, in which the hybrid ring and connecting stubs are also constructed of coaxial transmission line;

Fig. 7 illustrates a third specific embodiment of the invention, in which the hybrid ring and connecting stubs are constructed of wave-guide transmission line;

Fig. 8 illustrates a further specific embodiment of the invention, in which the hybrid ring and connecting stubs are constructed of wave-guide transmission line; v

Fig. 9 illustrates in diagrammaticform another specific embodimentof the invention in which two interterminal intervals are increased by a whole wavelength of transmission line; and

Fig. 10 illustratesin block schematic diagram form a further specific embodiment of the invention which constitutes a hybrid ring junction of the invention constructed of low frequency lumped-element networks. i

In more detail, in Fig. 1 ring, orclosed loop, Ill represents a closed ring, or loop, constructed of any suitable type'of transmission line such, for example, as coaxial, or waveguide, or two-wire, transmission line, having throughout the loop or ring substantially uniform mechanical and electricalcharacteristics and having a characteristic electrical impedance of Zn. .Such a ring or loop can, conveniently, be considered as comprising four arms connected in cascade to form the loop, with provisions, at each of. the four junction points between adjacent arms, for connecting external circuits to the four junctionpoints, respectively.

Points I, A, O and B represent points on the loop Ill at which stubs, or short sections, of transmission line, referred to hereinafter as terminals of the loop, .of the same kind as that of which loop [0 is constructed, are connected to the .transmissionlline constituting the loop [0. These connections can-all be of the shunt type or of the series type. (See, for example, Tyrrells above-mentioned patent for definitions and examples of series and shunt connections to twoconductor, coaxial and wave-guide transmission line.) Alternatively one or more of the connections can be series and the rest shunt conneotions, or vice versa.

As illustrated, three of the four interterminal spacings I8, I! and I8, can be ,alilre and are indi: cated as having a length Z. The urth intertere minal spacing I9 is then made (ii-M2,), where A is preferably the wavelength of the nominal or median frequency of the frequency range in which the device is intended to be used,

If the loop H3 is to have hybrid properties e my above-mentioned pendi e ap licat o Serial No. 789,935, now Patent No. 2,5313%? for the definition of hybrid properties) it must have wo pa s o coniueate re at rminal 1- e two pairs of terminals the two terminals of each pair being so related that energy introduced at one terminal of the pair will notleave the structure at the other terminal of the same pair. at the w pairs of erm al 1 an O, d A and B, are, respectively, conji gately related is obvious from inspection. For example, energy introduced at I will reach 0, by the two paths IE0 and 1A0, Since the lengths of these two paths differ by )\/2 the two portions of the energy introduced at I will arrive at Q exactly 189 degrees out of phase and no energy will leave the loop at terminal 0. The same situation exists with respect to the relation between terminals A and B. These and a number of other relations obtaining for hybrid structures are, of course, elementary and well understood by those skilled in the art and will not, therefore, he further discussed here.

The general problem to be solved connection with the present invention can be stated as fol lows: With a hybrid ring or loop of transmission line having a uniform characteristic impedance of Zn, as illustrated by the diagram of Fig. 1, what should the distance 1 be in order thata circuit having the arbitrary impedance ZA' (represented by impedances ll, l2, l3 and l l'of Fig. l, respectively) can be connected to the loop at each of the four points I, A, O and B without there beingintroduced at I will divide equally between the 2 two paths IE0 and IAO (since both paths have the same characteristic impedance Z6) and the two portions of the energy will arrive at O in phase opposition. The situation in such a case is precisely similar from an electrical standpoint to that which would exist if a short circuit were placed across the loop of transmission line at the point 0.

To facilitate consideration of the circuit of the diagram of Fig. 1 for the case in which energy is introduced into terminal point I, we can redraw it in straight-line form as shown in Fig. 2. That is, going from point I toward the right we find a length of transmission line I9 (Z+')\/2) lon before reaching point B. At point B we find two additional circuits connected, we will assume for the present analysis, in parallel. (It will be apparent as the analysis proceeds that a series con nection could equally well be. assumed.) Of the two additional circuits, one is a length of loop transmission line i8, Z long, terminated effectively (at point 0) in a short circuit, i. e., an impedance of zero, and the other is a circuit terminated in an impedance I i of Z As is well known to those skilled in the. art, if the linev connectingi-mped:

ance Z to point B. has a length of n t/ 2 where L .is any whole integer, the impedance of the circuit at point B will also be ZA. For all four terminal points I, A, O and B it will be assumed that the impedance ZA is effectively connected at its associated terminal point, or is connected by a line nx/ 2 long.

Similarly, going from point I toward the left we a length of line 16, Z long, before reaching point A and at A we find two impedances connected in parallel, one being the length of line l1, 1 long, terminated, effectively (at point 0), in a short circuit, the other being impedance l3, ZA.

Since we are, in this instance, interested only in the impedances, at point I, of the right and left portions of the circuit of Fig. 2, just described, we can omit the half Wavelength portion of member 19 of Fig. 2. This gives us directly the diagram of Fig. 3, i. e., we replace 19 of Fig. 2 by IQ of Fig. 3. Terminal points B and O at the right side of Fig. 2 are designated B'- and O in Fig. 3 and line I8 is designated 18 to indicate that, though the impedance has not been changed, the phase relations have been changed 180 degrees by removal of the M 2 length of line.

From the standpoint of impedance at point I, then, we have, effectively, like right and left portions, Fig. 4 representingthe left portion of the circuit of Fig. 3. Since these two portions are in parallel and are of the same impedance each must have an impedance of 22A at point I if the total impedance at terminal I is to be ZA, in accordance with the requirements stated the problem to be solved by the invention, above.

From the Radio Engineers Handbook," by F. E. Terman, published by McGraw-I-Iill Book Company, Incorporated, New York, 1943, Equation 62, at page 182, the impedance Zs at one end of a length of transmission line, having a characteristic impedance of Z0 and terminated at the other end in an impedance Z1. is the following:

where Z is the length of the line and A is the wavelength of the energy with respect to which the impedance is to be measured,

Dividing both the numerator and denominator 9 Equa ion. above by Y and setting 0=- we obtain Zr 1 tan 0 Applying this equation to the line section l8. of Fig- 4;, its impedance Z's at point B is tan 0 %+j tan 0 1+ 1 tan 9 since Z ,=O, (i. e., 18 is effectively short-oil! cuitedat 0-) Equation .3 du s o Z's=:i tan 0 (Z0) (4) Setting ZA=7CZO we have, for the, parallel com: bination of 2's and ZA at pointB of Fig. 4, I

is the impedance terminating line section l9" at point B of Fig. 4, so that for the impedance of line section [9 at pointI we obtain kj tan tan 0 tan 0. k+j tan o which reduces to 2Icj tan 0tan 0 [I i Z, k(l tan 0) +j tan 0 (7) Since the diagram of Fig." 3 is symmetrical, the impedance of the circuit to the left of point I will, as explained above, also have the impedance ZIIIS as given by Equation 'land, as is also explained above, in order for the impedance at point I to be ZA, it is obvious that i ZIIIS must equal 22A which in turn is 23:20, since ZA=7cZo.

Therefore: M

2kj tan 0tan 0 lc(1tan 0)+j tan 0 2kz0 (8) Dividing both sides of Equation 8 by Z0 and multiplying both sides by the denominator of the left-hand side, we obtain:

2M tan 0tan 0=2k (1tan 0) +27cj tan 0 (9) whence tan 0=27c (1tan 0) (10 in Equation 13, tan 0 becomes indeterminate, For values of 1c less than in Equation 13, .tan 0 becomes imaginary. For any valueof k which is greater than Vi (approximately 0.707) inEquation 1s, tan a is real.

This means, obviously, that the arbitrary 1mpedance, ZA, chosen to terminate the iour arms of a hybrid ring constructed of transmission line whence By way of specific illustrative examples,values of the interterminal length Z, for eight valuesof k are tabulated below.

Table. I

k tan 0 0 1 Degrees 5. 3 79. 3 .2203 i 3. 0 71. 5 1986) 2. 1367 65 180% 1.414 I 55 k 1. 143 48. 8 {136A 1. 016 45. 5 1264k 1. 010 45. 3 .1258) 1. 000 45. 0 1250A From inspection of the above-tabulated data, it is apparent that four-terminal hybrid rings of the invention constructed of uniform transmission line having a characteristic impedance of Zn, in which three of the interterminal spacings are alike and fall within the'range of approximately maximum to /9 minimum, inclusive, and the fourth interterminal spacing of which exceeds the other three by /2A, .will have the property that all terminals canbe connected to circuits having the same impedance; The precise value of this impedance for any particular structure, 'of course, can be determined from the above Formulas l3 and 14 as described above.

As will be described below in detail, in connection with specific illustrative structures, in any hybrid ring structure of the invention, all four interterminal spacings can be increased by any desirednumber of additional half wavelengths without disturbing the balance or terminal impedances of the structure. Also, any one or more of the four interterminal spacings of a hybrid ring structure of the invention can be increased by one or more full wavelengths, independently of the other interterminal spacings, without disturbing the balance or termina impedances of the structure.

From Table I above, of values of k, 0 and 1, it is also apparent that as k is increased, 0 approaches i5 degrees as a limit and Z approaches /8) For most practical purposes, where is exceeds 5, I can be taken as 1 without introduc ing any significant unbalance or impedance irregularities.

This means that for most purposes, any value of ZA that is at least in the order of five times or more larger than the Zo'of the hybrid ring transmission line can be employed with aring having three interterminal intervals of i each and the fourth interval of 4,1.

By way of further illustration, a few specific structures of the invention will now be described in detail. 1 1 i where the wave-guide transmission line from which the ring is formed, 1. e., the sides can be, for example, each approximately and the innermost and outermost surfaces of the ring are each approximately A,) (transverse dimensions).

The four terminals 62 to 65, inclusive, respectively, connect to the periphery of ring 60 as shown. Three interterminal spacings (A, B and C) measured along the center line of the side of the ring 60 are .651 (center to center) and the fourth (D) is 1.15)\. v

To obtain wave-guide hybrid rings of larger size of either one ofthe two types illustrated by Figs. 7 and 8 which will retain the equality of terminal impedances, it is simply necessary to increase all four interterminal spacings A, B, C and D by the same integral number of half wavelengths necessary to produce a ring of the size desired. Also, as described above in connection with coaxial structures, any one or more of the interterminal spacings can be increased by any number of whole wavelengths, as may be.

deemed convenient, without affecting the desirable properties of the structure.

The above-described four specific structures of Figs. to 8, inclusive, have obviously been based greater than the other three. Designating the three equal spacings as Z, as shown in Fig. 1, the fourth is then As explained in detail above,

Equation 14, where 0 can be determined from Equation 13, i. e.,

Zozthe characteristic impedance of the trans-- nal spacings or intervals-can be increased by one or more full wavelengths without disturbing-the balance or impedance relations of a structure of the invention, we can state the requirements generally by the following relations:

n=0 orany whole positive integer and must be the same for all four spacings.

mz'O or any whole positive integer and need not be the same for any two of the four spacings.

In Fig. 9, the arrangement of a further form of hybrid ringof the invention, in which the impedance ZA connected to the ring at each of the junction points I, A, O, B, can be of any value greater thanfive times the characteristic impedance Z0 of the transmission line of which the ring is constructed, is shown. As shown, the interval between points I and A is 1%) The interval between points A and O is as is also that between points 0 andB. The interval between points I and B is l% Obviously, the intervals between I and A and between I and B each includes a full extra wavelength in addition to the minimum required length of transmission line for these intervals. As mentioned hereinabove, as long as the impedances of all four circuits connected to the four junctionpoints I, A, O and B;

respectively, are of the same impedance and are greater than five times the characteristic impedance of the transmission line of which the ring is constructed, there will be substantially no impedance mismatch at any of the four junction points. i

In Fig. 10, a hybrid ring, or loop, of the invention, th fourarms of which are composed of lumped element networks, is shown. Such hybrid rings, or loops, can be .employed in frequency ranges where the suitable lengths of simple transmission lines to compose such a ring, or loop, are of inconveniently great length.

The four arms comprising the f our-terminal i. networks 200, 20!, 202 and '203 are variously the fact that any one or more'of the 'intertermi 165 above.

known as artificial lines or delay networks and are constructed of lumped elements (i. e., coils, condensers, and in some instances resistances also) in accordance with principles long well known in the, art. For operation of the resulting hybrid structure over relatively narrow frequency ranges, these networks can be of the simple forms illustrated, by way of example, in Fig. ,7 of United states Patent 2,410,144, granted .October 29,1946, to W. A. Tyrrell, assignor to applicants assignee. For hybrid rings, or loops, to operate over relatively wide-band frequency ranges, the more complex type of all-pass delay networks described at page 8, columns 1 and 2 of United States Patent 1,828,454, granted October 20, 1931, to H. W. Bode, assignor to applicants assignee, can preferably be employed. Networks 200, Zlll and 202 are each designed to have, over the frequency band in which they are to be employed, the phase characteristic postulated by Equation 15 above. .Likewise, network 293 is designed to have over the same frequency band the phase characteristic postulated by Equation 16 As explained by the above-mentioned patent 2,445,895 of W. A. Tyr'rell in connection with Figs. 2 and 4 of the patent, wave-guide connections in the E plane (such as are used in the structure of Fig. 7 of the present application) are effectively series connections and wave-guide connections 11 in the H plane (as in the structure of Fig. 8 of the present application) are effectively parallel connections.

Any of the numerous and varied alternative types of connections well known to the art, including those disclosed in Tyrrells above-mentioned patent, can obviously be used in structures of the invention in place of the types shown in Figs. to 8-, inclusive, of .the present application without departin from the spirit and scope of the invention.

Likewise, numerous and varied special types of transmission lines or wave guides can be employed in the construction of hybrid rings or loops of the instant invention. Indeed, the rings or loops need not be circular but can, obviously, be oval, rectangular, or of irregular shape so long as the prescribed eiiective electrical lengths of the four arms of the loop are obtained.

No attempt has here been made to exhaustively cover the full range of equivalents since these will readily occur to persons skilled in the art.

What is claimed is:

'1. An electrical hybrid junction adapted'to join four external electrical circuits, each having a predetermined impedance of Zn, said junction comprising a, closed loop-"oi uniform transmission line having a characteristic impedance of Z0 and four connection points spaced along said loop, three of the intervals between said connection points along said loop, 'each being and the fourth interval being N Z k where -49 is the angle whose tangent is is the wavelength of the energy to be transmitted through the junction, is is the ratio of impedance ZA to impedance Z0 and is greater than n is zero or any positive integer and is the same for all 'four intervals, "and m is zero or any positive integer and need not be the same for any two or more of the four intervals.

2. An electrical hybrid junction adapted to join four external electrical circuits, each having a predetermined impedance of Zn, said junction comprising a closed loop of unii'ormtran'smission line having a characteristic impedance of Z0 and four connection points spaced along said loop, three of the intervals between said connection points each being 15x, the fourth interval between connection points being .'657\ where x is the wavelength of the energy to be transmitted through said junction.

3. The hybrid junction of claim 2 in which all four interconnection point intervals "are increased in length by where n is any positive integer.

4. The hybrid junction of claim 2 in which one or more of the four interconnection point interand the electrical length of the fourth arm is N9 7\ 5 1+ ilwhere 0 is the angle Whose tangent is A is the wavelength of the energy to be transmitted through the junction, :k is the ratio of a predetermined impedance ZA, assigned to tour external circuits to whichthe four interarm junction points are to be connected, respectively, to the characteristic impedance Z0, 70 being greater than n is rzero or a positive integer and is the same for all four arms, and "m is zero or any positive integer and need not be the same for any two or more of the four arms.

6. The junction of claim 1., in which the uniform transmission line .is of the coaxial type.

'7. The junction of claim 1, in which the uniform transmission line is of the wave-guide type.

8. The junction of claim 2, in which the uniform transmission line is of the coaxial type.

9. The junction of claim 2., in which all four interconnection point intervals are increased in length by where n is the same for all intervals and is any positive integer and the uniform transmission line is of the wave-guide type.

1-0. The junction :of claim 2, in which all four interconnection point intervals are increased in length by where n is the same for all intervals and is any positive integer, and any of the four interconnection point intervals are additionally increased by "mi where m is any positive integer and need not be the same for any two of the intervals.

WILLARD D. LEWIS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,147,809 Alford Feb. .21., 1939 2,436,828 Ring Mar. 2, 1948 2,445,895 Tyrrell July .27, 1948 FOREIGN PATENTS Number Country Date 615,355 Great Britain Jan. 5, 1949 

